This invention relates to improved rust preventative compositions for use in low-foaming aqueous formulations. Such compositions comprise a partial amide of a selected alkanolamine and an unsaturated dicarboxylic acid, together with an alkanolamine salt of an aliphatic dicarboxylic acid.
Corrosion is a major problem in automotive and industrial systems where water is a likely component of liquid systems. While many anti-rust formulations have been marketed through the years, there remains a need for an economically attractive yet highly effective reagent system. Problems usually have involved limited water solubility, scum formation in hard water, extensive foaming, and the like. Water-based systems are generally preferred to hydrocarbon-based systems for reasons of cost and safety. A widely used corrosion inhibitor system comprises sodium nitrite and triethanolamine.
However, systems of the hydrocarbon-based and nitrite types pose environmental problems. Use of nitrite systems is of particular concern because of potential hazards in the work place due to possible generation of nitrosamines, particularly when used in metalworking applications where elevated temperatures develop from the friction of metal-to-metal contact. Replacement of nitrite reagents with monoalkanolamide borates is set forth in Waldstein U.S. Pat. Nos. 3,969,236 and 4,176,076. Another approach, employing sulfonamide derivatives, is described in Widder, et al., U.S. Pat. No. 4,344,862. The present status of water-based metalworking lubricants is reviewed by Hunz in Lubricating Engineering, vol. 40, no. 7, pp. 549-553 (1984).
In addition to their importance in water-based metal-working fluids, anti-rust applications range from corrosion inhibition in gasolines and fuel oils where water is a trace component to use in cooling systems employing water as a coolant or as a recycle stream. Other formulations find use in oil well drilling and in soluble oils.